This application claims the benefit of Korean Patent Application No. 1999-01699, filed on Jan. 20, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to an image detector and, more particularly, to a thin film transistor (TFT) type optical sensor with a conductive object or living object detection pattern.
2. Discussion of the Related Art
Generally, a thin film transistor type optical sensor comprises a window for receiving light reflected from an object, a sensor TFT for generating an optical current in proportion to the intensity of the light, a storage capacitor for storing charges of the optical current transmitted from the sensor TFT as charged information, and a switching TFT for outputting the charged information stored in the storage capacitor in accordance with an external control signal.
FIG. 1 shows a conventional TFT type optical sensor.
A sensor S1 is coupled to a controller 2 whose output end is coupled to an input end of an electrical power source 4. An output end of the electrical source 4 is electrically coupled to both the sensing part 6 and a light source 8. The sensor S1 may be replaced with a mechanical switch or an infrared switch. In operation, when a signal is output from the sensor S1, the controller 2 transmits the signal to the sensing part 6 and the light source 8 through the electrical power source 4.
FIG. 2 shows another conventional TFT type optical sensor using a mechanical switch SW1 instead of the sensor S1.
One end of the switch SW1 is coupled to an input end of the electrical power source 4 and the other end to an input end of a controller 2. An output end of the controller 2 is coupled to an input end of the electrical power source 4 whose output end in turn is coupled to both a sensing part 6 and a light source 8.
In operation, when the switch SW1 is turned xe2x80x9cONxe2x80x9d to operate the optical sensor, electrical power is supplied from the electrical power source 4 to the controller 2, then input to the electrical power source 4 as a predetermined control signal. Next, the electrical power source 4 transmits electrical power to the sensing part 6 and the light source 8.
The two above-described conventional TFT type optical sensors have the following drawbacks:
1. When the switch is turned ON, since electrical power is always supplied, electrical power is unnecessarily consumed even when the sensor is not detecting an object.
2. They have no means for recognizing whether an object is living or not. For example, the sensor may be a fingerprint detection device, In that case, it is important for the sensor to discriminate between a live human finger, and, for example, a photograph or photocopy of a human fingerprint. Otherwise, the fingerprint detection device may be spoofed.
Accordingly, the present invention is directed to an image detector that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
It is an objective of the present invention to provide a TFT type optical sensor that uses a minimal amount of electrical power and can recognize whether an object is living or not.
To achieve the above objective, in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides a TFT type optical sensor with a conductive object detection pattern, having a backlight and a sensing part to which electrical power is supplied only when the detection of an object is carried out. By detecting whether and to what degree the object is conductive, the a TFT type optical sensor can detect a living object.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.